Dynamic hydraulic fluid stimulation regulated intramedullary pressure ☆

Physical signals within the bone, i.e. generated from mechanical loading, have the potential to initiate skeletal adaptation. Strong evidence has pointed to bone fluid flow (BFF) as a media between an external load and the bone cells, in which altered velocity and pressure can ultimately initiate the mechanotransduction and the remodeling process within the bone. Load-induced BFF can be altered by factors such as intramedullary pressure (ImP) and/ or bone matrix strain, mediating bone adaptation. Previous studies have shown that BFF induced by ImP alone, with minimum bone strain, can initiate bone remodeling. However, identifying induced ImP dynamics and bone strain factor in vivo using a non-invasive method still remains challenging. To apply ImP as a means for alteration of BFF, it was hypothesized that non-invasive dynamic hydraulic stimulation (DHS) can induce local ImP with minimal bone strain to potentially elicit osteogenic adaptive responses via bone-muscle coupling. The goal of this study was to evaluate the immediate effects on local and distant ImP and strain in response to a range of loading frequencies using DHS. Simultaneous femoral and tibial ImP and bone strain values were measured in three 15-month-old female Sprague Dawley rats during DHS loading on the tibia with frequencies of 1 Hz to 10 Hz. DHS showed noticeable effects on ImP induction in the stimulated tibia in a nonlinear fashion in response to DHS over the range of loading frequencies, where they peaked at 2 Hz. DHS at various loading frequencies generated minimal bone strain in the tibiae. Maximal bone strain measured at all loading frequencies was less than 8 με. No detectable induction of ImP or bone strain was observed in the femur. This study suggested that oscillatory DHS may regulate the local fluid dynamics with minimal mechanical strain in the bone, which serves critically in bone adaptation. These results clearly implied DHS's potential as an effective, non-invasive intervention for osteopenia and osteoporosis treatments. © 2013 Published by Elsevier Inc. Introduction Aging or functional disuse of the bone can subsequently create a number of physiological or pathophysiological changes in the skeleton of the affected subjects (e.g. elderly, long-term bed-rest patients, and astronauts who participate in long-duration spaceflight missions), leading to conditions such as osteopenia As a potent regulator in bone adaptation, bone fluid flow (BFF) with altered velocity or pressure acts as a communication media between an external load and the bone cells, which then regulate bone remodeling Therefore, ImP-induced BFF provides a great potential in developing novel mechanical stimuli as countermeasures for disuse bone loss. Previous in vivo study using oscillatory electrical muscle stimulation (MS) in a hindlimb suspension (HLS) functional disuse rat model has demonstrated that oscillatory MS-induced muscle contraction can generate ImP and bone strain to mitigate disuse osteopeni

Mechanobiological Modulation of Cytoskeleton and Calcium Influx in Osteoblastic Cells by Short-Term Focused Acoustic Radiation Force

Mechanotransduction has demonstrated potential for regulating tissue adaptation in vivo and cellular activities in vitro. It is well documented that ultrasound can produce a wide variety of biological effects in biological systems. For example, pulsed ultrasound can be used to noninvasively accelerate the rate of bone fracture healing. Although a wide range of studies has been performed, mechanism for this therapeutic effect on bone healing is currently unknown. To elucidate the mechanism of cellular response to mechanical stimuli induced by pulsed ultrasound radiation, we developed a method to apply focused acoustic radiation force (ARF) (duration, one minute) on osteoblastic MC3T3-E1 cells and observed cellular responses to ARF using a spinning disk confocal microscope. This study demonstrates that the focused ARF induced F-actin cytoskeletal rearrangement in MC3T3-E1 cells. In addition, these cells showed an increase in intracellular calcium concentration following the application of focused ARF. Furthermore, passive bending movement was noted in primary cilium that were treated with focused ARF. Cell viability was not affected. Application of pulsed ultrasound radiation generated only a minimal temperature rise of 0.1°C, and induced a streaming resulting fluid shear stress of 0.186 dyne/cm2, suggesting that hyperthermia and acoustic streaming might not be the main causes of the observed cell responses. In conclusion, these data provide more insight in the interactions between acoustic mechanical stress and osteoblastic cells. This experimental system could serve as basis for further exploration of the mechanosensing mechanism of osteoblasts triggered by ultrasound

Fourier-Bessel field calculation and tuning of a CW annular array

A 1-D Fourier-Bessel series method for computing and tuning the linear lossless field of flat continuous wave (CW) annular arrays is given and discussed with both numerical simulation and experimental verification. The technique provides a new method for modelling and manipulating the propagated field by linking the quantized surface pressure profile to a set of limited diffraction Bessel beams propagating into the medium. In the limit, these become a known set of nondiffracting Bessel beams satisfying the lossless linear wave equation, which allow us to derive a linear matrix formulation for the field in terms of the ring pressures on the transducer surface. Tuning (beamforming) of the field then follows by formulating a least squares design with respect to the transducer ring pressures. Results are presented in the context of a 10-ring annular array operating at 2.5 MHz in water

Calculated Dynamic Parameters for Different Acoustical Power.

<p>Notes. Values for velocity and τ represent mean ± SE. The radius of the focal region is 0.2 mm. Efficiency of power conversion is 68.8%. Fluid shear stress and radiation force were calculated according to both formulas (see text for details).</p

Schematic diagram of experimental setup for spatiotemporal measurements of the effects of acoustic radiation force on MC3T3-E1 cells.

<p>The setup includes an inverted microscope and a high intensity focused ultrasound system. Movement of the spherical transducer is controlled by the three-dimensional support framework.</p

Measured average ultrasound-induced temperature rise vs. duration of different acoustical power and stimulation modes.

<p>Error bars (30-s intervals) show the standard deviation between the different measurements. Temperature was measured with a thermocouple probe immersed in the culture medium.</p

Changes in fluorescence intensities of MC3T3-E1 cells loaded with Calcium GreenTM-1.

<p>Time-lapse sequence images showing calcium influx in the cells before pulsed ultrasound radiation (A), at the start (B) of radiation and during the radiation (C and D). Compared to cells without ultrasound radiation, the pulsed ultrasound evoked a significant increase in intracellular calcium levels (E). Dotted lines represent duration of radiation on- and off-switch, respectively. Scale bar, 10 µm.</p